Spatial modelling of landscape-scale vegetation dynamics, Mont Do, New Caledonia

G.L.W. Perry; N.J. Enright

The coniferous tree Araucaria laubenfelsii forms a key component of vegetation structural assemblages on ultramafic substrate at Mont Do, New Caledonia. It is the sole species to be found both as an emergent in maquis and as a common canopy species in adjacent rainforest patches. This paper describes a spatially explicit, landscape-level model developed to investigate the vegetation pattern on Mont Do and provides preliminary results of model analyses. Results indicate that the interaction between fire, terrain and the long residence times of fire-prone successional stages may be largely responsible for the landscape patterns visible. Maquis is found predominantly on hillsides where fire spread is likely to be most rapid, while maquis with emergent A. laubenfelsii, and A. laubenfelsii woodland, are restricted to rocky areas and rainforest margins of likely intermediate fire frequency. The model indicates that if fires were to become either more frequent or increase in size, maquis would become increasingly prevalent in the landscape. Pattern metrics, such as fractal dimension, indicate that as a result of such a change, the spatial complexity and fragmentation of the landscape may be reduced. Conversely, if fire frequency decreases or fire sizes become smaller, then rainforest becomes more dominant. Although the presence of A. laubenfelsii on Mont Do is not threatened under such a scenario, the persistence of certain 'transient' structural assemblages at their current abundances seems less certain. While the role that ultramafic soil conditions might play at the landscape level is not clear, several possible interactions between the plant-soil relationship and broader scale dynamics are identified. In particular, soil chemical constraints on plant growth may be responsible for the very long time-scales associated with succession from maquis to forest, and this slowed succession increases the potential role of fire as a major determinant of landscape-scale vegetation pattern relative to that on nearby non-ultrabasic substrates.

Spatial modelling of landscape-scale vegetation dynamics, Mont Do, New Caledonia

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